In recent years, PC servers and UNIX servers of rack-mounting type, in which a plurality of server modules are stacked in layers on a rack cabinet, are the mainstream. At least one integrated circuit element (LSI), such as a central processing unit (CPU), is mounted on each server module. In a single server and a personal computer, a fan is provided immediately above a component that generates a large amount of heat, such as a CPU or an LSI, to cool the component with air, achieving stable operation. However, in rack-mounting type servers, in order to realize high performance and compact configuration, as many server modules as possible have to be stacked on a single rack cabinet. Because the thickness of the server modules has to be reduced, in server modules of rack-mounting type, it is difficult to directly attach a fan to a component that generates a large amount of heat, such as a CPU or an LSI. Furthermore, because the server modules are stacked, it is difficult to release heat in the server modules to the outside. To solve these problems, there have been proposed means for cooling CPUs and LSIs, in which refrigerant is circulated on heat-generating components, such as CPUs and LSIs, to cool these components, and the refrigerant having absorbed heat from the CPUs and the LSIs is circulated with a pump to a radiator to be cooled with a cooling fan.
The following is reference document.    [Document 1] Japanese Laid-open Patent Publication No. 2004-319628